In the following disclosure, positional terms such as “above” and “below” are used with reference to a gun in its normal firing position, that is, positioned to shoot “forward” (away from the shooter) in a generally horizontal plane.
Dust covers for hand-held firearms have long been known in the art, especially from their use with handguns that have a housing. Example uses include covering the magazine opening, (e.g., the submachine gun MAS Mod. 1938) or the ejection opening (e.g., the assault rifle 44) of the firearm. In the case of a magazine dust cover, the dust cover employs a mechanical locking device such as a simple catch piece that may be opened and closed by hand. In the case of an ejection opening dust cover, the action of a spring causes the dust cover to open automatically when the moving breechblock opens the mechanical locking device. When not firing or when handling the gun, the ejection door may be closed by hand.
In traditional guns, the housing is made of steel or sheet metal that is sufficiently rigid to ensure a faultless operation of the locking device, even if the housing is constantly stressed by the spring when the dust cover is in the closed position.
Modern guns, however, often employ a plastic housing in which an expanded metal insert is added proximate to the locking device so that the locking device will seat properly. With improvements in design and construction, plastic housings have become more and more lightweight and, accordingly, more and more flexible. As a result, a housing of this type becomes temporarily deformed in a noticeable manner if, for example, the gun falls on the ground or strikes a solid obstacle with sufficient force. This deformation can cause the locking device to disengage in an undesired manner, so that the aforementioned cover opens just when the danger of foreign object entry is especially great. For example, dirt may enter the uncovered opening if the gun were to impact with a hard surface, such as a floor.
In housings with two ejection openings (for right-handed or left-handed marksmen), the opening that is not in use should remain closed in order to prevent possible damage that could otherwise result from, for example, sand or dust entering the gun. Moreover, as a general rule during operation, the marksman checks the used ejection opening only, and does not check the unused one.
To improve operation, expanded reinforcements could be embedded around the ejection opening and into the dust covers. However, these measures would be counter-productive because they would cause an increase in the weight of the housing. Another option would be to redesign the locking device so that it supports larger tolerances. This would mean, however, an increase in the cost of the firearm. Also, the required space is often not available.